As one type of fuel cell, a polymer electrolyte fuel cell (PEFC) is known. The polymer electrolyte fuel cell, as shown in FIG. 8, comprises a membrane electrode assembly (MEA) 15 as a main component. The membrane electrode assembly 15 is placed between a separator 14 having a fuel (hydrogen) gas channel and another separator 14 having an air gas channel, thus forming a single fuel cell 20 referred to as a single cell. The membrane electrode assembly 15 comprises an electrolyte membrane 5, which is an ion exchange membrane. On one side of the electrolyte membrane 5, there are stacked an anode-side electrode (catalyst layer) 12a and a diffusion layer 13a. On the other side, there are stacked a cathode-side electrode (catalyst layer) 12 b and a diffusion layer 13b. 
For electricity generation, as air is supplied to the cathode-side separator and fuel (hydrogen) is supplied to the anode-side separator, a reaction H2→2H++2e− proceeds at the anode, and a reaction ½O2+2H++e−→H2O proceeds at the cathode side. The extent of such chemical reactions should desirably be uniform regardless of their locations in the electrodes. However, since the concentration of the gases (H2, O2) varies at the entry and exit sides as the reactions proceed, the electricity generation distribution inevitably becomes non-uniform if the ion conductivity of the electrolyte membrane is uniform over its entire surface.
The magnitude of ion conductivity is generally expressed by ion-exchange group equivalent weight (EW value); an electrolyte membrane with a high EW value has low ion conductivity, while an electrolyte membrane with a low EW value has high ion conductivity. In a polymer electrolyte fuel cell, typically an electrolyte membrane with an EW value that is smaller than 1500 is used. In order to overcome the aforementioned problem, i.e., to make the electricity generation distribution in the electrode surface as uniform as possible, Patent Document 1 and Patent Document 2, for example, propose the use of ion exchange resins having different EW values as the electrode or catalyst layer at the gas entry and exit sides.
In the polymer electrolyte fuel cell described in Patent Document 1, catalyst dispersed liquids are prepared with two ion exchange resins having different ion exchange capacities. The two catalyst dispersed liquids are applied to different regions to form an electrode surface such that the ion exchange capacity of the ion exchange resin at the exit side of the oxygen electrode becomes smaller than the ion exchange capacity of the ion exchange resin at the gas entry side. Namely, when forming a single cell, the EW value of the ion exchange resin at the gas entry side is made high, while the EW value of the ion exchange resin at the exit side is made low. Patent Document 2 discloses a similar technique, by which two kinds of slurry-like catalyst powder containing solutions prepared with ion exchange resins having different EW values are applied separately to form an electrode.
Patent Document 1: JP Patent Publication (Kokai) No. 2001-196067 A
Patent Document 2: JP Patent Publication (Kokai) No. 2002-164057 A